Recently, in passenger vehicles such as an aircraft, various in-flight services are provided to passengers by an in-flight entertainment system called IFE (In-Flight Entertainment), which is installed and disposed in an aircraft or in a cabin. When passengers use such in-flight services, for example, the passengers can view and listen to distributed movies or music by using a video display section of a liquid crystal display device or a headphone handed out when they board the aircraft. Furthermore, similarly, by using an operating terminal called a handset provided in each seat, passengers can play a game, make a phone call to the outside of the aircraft, and receive connection services to the Internet (see, for example, Patent Documents 1 and 2). Such services are transmitted as digital data via a network transmission path from an AV server set in an aircraft to a seat terminal (IFE) provided in each seat.
Hereinafter, a conventional AV content view system in an aircraft is described with reference to FIG. 5. FIG. 5 is a view showing an entire configuration of conventional AV content view system 200.
In AV content view system 200, network transmission path 2 is laid out along a plurality of seats 1m and 1n. Network transmission path (hereinafter, referred to as “transmission path”) 2 is connected to AV server 3. AV server 3 provides AV content including video and audio content, for example, movies and games. Furthermore, AV server 3 can provide flight information and the like, if necessary.
Transmission path 2 is made of Ethernet (trade mark) cable. To transmission path 2, seat terminals 14m and 14n are connected for each seat. Furthermore, video display section 6m, 6n such as a liquid crystal display is set on the back part of each seat, and controller 5m, 5n and headphone 7m, 7n are connected to the front part of the seat. These devices are connected communicably to the above-mentioned AV server 3 via seat terminals 14m and 14n. 
Furthermore, microphone 8a in crew's cabin 8 is connected to transmission path 2 via IP (Internet Protocol) adaptor 8b configured to convert an analog audio signal into a digital audio packet and to connect it to the Ethernet (trade mark).
A microphone similar to microphone 8a is equipped in a cockpit (not shown), and cabin attendants and an airline captain make an in-flight announcement to passengers by using the microphone.
In such a configuration, when, for example, a passenger seated in seat 1m selects a movie which he/she wants to watch by operating controller 5m, video and audio of the movie are downloaded and stored in seat terminal 14n of seat 1n in front of the passenger from AV server 3 (a plurality of pieces of content may be stored in a seat terminal in advance).
Video of a movie selected by a passenger is displayed on video display section 6n of front seat 1n, and audio is transmitted as digital data (audio packet) to seat terminal 14m behind seat terminal 14n via transmission path 2 and demodulated into an original analog audio signal in seat terminal 14m. A passenger can listen to the analog audio by headphone 7m. 
The above-mentioned in-flight announcement from cabin attendants or an airline captain can be listened to by headphone 7m via seat terminal 14m of seat 1m. The in-flight announcement can be also listened to from a loudspeaker provided on the ceiling. However, a passenger using headphone 7m for a movie and the like cannot listen to the announcement from the loudspeaker. Therefore, the in-flight announcement is transmitted to seat terminal 14m via transmission path 2, and the audio of the movie is automatically switched to the in-flight announcement in the seat terminal, so that the in-flight announcement can be listened to by head phone 7m. 
However, with the above-mentioned conventional AV content view system in an aircraft, passengers can receive only services of the AV content contained in AV server 3. Since there is a limit to the containing capacity of AV server 3, passengers using AV services repeatedly do not have content to be appreciated, or some passengers may not interested in the content.
Recently, portable terminals with which users can enjoy video and audio outside or in a mobile unit are being popularized. In a storage section (a hard disk or a semiconductor memory) of such a portable terminal, compressed data of AV content have been stored in advance. For example, users carry their portable terminals to the outside after they downloaded desired AV content into their portable terminals from PC and the like.
When passengers use such portable terminals in an aircraft, since the passengers use headphones attached to the portable terminals, they may miss in-flight announcement. Furthermore, although a large liquid crystal display for viewing AV services is equipped in front of the passengers, the passengers cannot use such a display and inconveniently watch video in a small screen of the portable terminal.    [Patent Document 1] Japanese Patent Application Unexamined Publication No. H7-143083    [Patent Document 2] Japanese Patent Application Unexamined Publication No. 2006-246297